vi characteristics of scr

VI CHARACTERISTICS OF SCR

(Model No : PEC16M1B)

User Manual

Technical Clarification /Suggestion :N / FTechnical Support Division,Vi Microsystems Pvt. Ltd.,

Plot No :75, Electronics Estate,Perungudi, Chennai - 600 096, INDIA.Ph: 91- 44-2496 3142, 91-44-2496 1852Mail : [email protected],Web : www.vimicrosystem

Version 1.0

mailto:[email protected],

CONTENTS

CHAPTER - 1 INTRODUCTION 1

1.1 Introduction 2

CHAPTER - 1 ABOUT OUR TRAINER 3

2.1 About Our Trainer 4

2.2 Front Panel View 5

2.3 Front Panel Description 6

2.4 Specification 6

CHAPTER - 3 EXPERIMENTAL SECTION 7

3.1 Vi Characteristics of SCR 8

CHAPTER - 4 THEORETICAL CONCEPT 11

4.1 SCR Power Circuit 124.2 SCR Characteristics 134.3 Device Testing Procedure 154.4 Precautions 16

VI CHARACTERISTICS OF SCR PEC16M1B

Vi Microsystems Pvt. Ltd., [ 1 ]

Chapter - 1

Introduction



1.1 INTRODUCTION

Power electronics deals with the applications of solid-state electronics for the control and

conversion of electrical power. Conversion techniques require the switching ON and OFF of

power semiconductor device.

An ideal power device should have no switching-ON and OFF limitations in terms of turn-ON

time, turn-OFF time, current and voltage handling capabilities. Power semiconductor technology

is rapidly developing with development in fast switching power devices with increased voltage

and current limits.

Power switching devices such as power BJTs, power SCRs, GTOs and other semiconductor

devices find increasing applications in a wide range of products. The applications of modern

microprocessors in synthesizing the control strategy for gating power devices to meet the

conversion specifications are widening the scope of power electronics. In this manual we shall

discuss about the VI characteristics of SCR.



Chapter - 2

About Our Trainer



2.1 ABOUT OUR TRAINER

The following is front panel of the PEC16M1B module. The Module PEC16M1B consist ofSCR VI-characteristics circuit.

Fig - 1. Pictorial View of PEC16M1B



2.2 FRONT PANEL VIEW

Fig - 2. Front Panel View



2.3 FRONT PANEL DESCRIPTION

SCR VI characteristics Trainer module consists of

1. SCR power circuit.2. SCR power supply circuit.3. Gate trigger voltage circuit.

* Input AC voltage is stepped down to 24V AC and rectified to DC voltage signal.

* Variable input (0 - 24V) DC is given using the VOLT. ADJUST POT provided on the

DC2front panel. Switch (SW2) controls V input voltage.

* Input AC voltage is stepped down to 18V and rectified. The rectified voltage signal isregulated to provide (0-15V) DC to the gate of SCR.

* The gate current adjustment can be made using the coarse and fine adjustment POT.

DC1Switch (SW1) controls the V input voltage.

g* Ammeter between P5 and P7 is to read the gate current (I ). Ammeter between P8 and

AP11 is to read the device current (I ).

AK* Voltmeter across SCR (between P9 and P10) is to read the device voltage (V ).

2.4 SPECIFICATION

DC1* Gate voltage (V ) - 0 to 15V

DC2* Supply Voltage (V ) - 0 to 24V

* SCR - TYN612 (600V/12A)

L* Load Resistance (R ) - 220 S / 50W



Chapter-3

Experiment Section



3.1 EXPERIMENTAL SECTION

EXPERIMENT - 1

AIM

To study the VI characteristics of SCR with positive gate current by using PEC16M1B trainermodule.

APPARATUS REQUIRED

i. PEC16M1B Module.ii. Ammeter (0 to 20 mA)mc -1 No

Ammeter (0 to 200 mA)mc-1 Noiii. Voltmeter (0 - 30V) - 1 No.iv. Patch Chords.

CONNECTION PROCEDURE

1 3 2 4i. Connect connector P to P and P to P .

5 7ii. Connect the ammeter between P and P connectors.

8 9iii. Connect the voltmeter between P and P connectors.

10 11iv. Connect the ammeter between P and P connectors.

12 14 13 15.v. Connect connector P to P and P to P

EXPERIMENTAL PROCEDURE

i. Switch on the 230V AC supply.

Gii. Now vary pot3 and set the gate current (I ) in the range of 3mA to 4mA.

AKiii. Now slowly increase the anode-cathode voltage (V ) by varying the pot 4 till the thyristor

A AKget turned on, note down the ammeter (I ), Voltmeter (V ) readings.

BRiv. Now find out Break over voltage(V ).

v. For various gate current take the reading and tabulate in table 1.

AK Avi. Plot the graph V Vs I in a graph sheet.



vii. After note down the max anode current remove the gate current by switch OFF the switch

1 S .

akviii. Now reduce the anode cathode voltage(V ) gradually, at on stage the anode current will

H suddenly reach zero value. The current at this stage is holding current (I ).

1 akix. Now switch ON the switch S and increase anode cathode voltage (V ) slightly, now again

1switch OFF S .

1a. If the anode current shows zero value again switch ON S and vary the anode cathodevoltage.

b. If the anode current shows some value, that is the latching current of the SCR.

TABLE

L HI = (mA) I = (mA)

S.Nog I = (mA)

AK AV (V) I (mA)



MODEL GRAPH



Chapter - 4

Theoretical Concept



4.1 SCR POWER CIRCUIT

A thyristor is one of the most important types of power semiconductor devices. Thyristors areused extensively in power electronic circuit. They are operated as bistable switches, operatingfrom non conducting state to conducting state. Thyristor can also called as SCR (siliconcontrolled Rectifier). A SCR is a four layer three terminal semiconductor switching device ofPNPN structure with three PN-Junctions. The three terminals are anode, cathode and gate Thethyristor symbol and the sectional view of PN junctions are shown below. SCRs aremanufactured by diffusion.

Cross section view of thyristor Symbol of thyristor

When the anode voltage is made positive with respect to the cathode, the junction J1 and J3 areforward biased. The junction J2 is reverse biased and only the small leakage current flows frompositive to negative. The thyristor is then said to be in forward blocking or off-state conditionand the leakage current is known as off-state current ID. If the anode-to-cathode voltage VAK

is increased to a sufficiently large value. The reverse biased junction J2 will break. This isknown as avalanche breakdown and the corresponding voltage is called forward breakdownvoltage VBO. Since the other junctions J1 and J3 are already forward biased. There will be freemovement of carriers across all three junctions, resulting, in a large forward anode current. Thedevice will be in a conducting state or on state. The voltage drop would be due to the ohmic dropin the four layers and it is small typically 1V. In the on state, the anode current is limited by anexternal impedance or a resistance RL shown in figure. The anode current must be more then

La value known as latching current I . In order to maintain the requires amount of carrier flowacross the junction. Otherwise, the device will revert to the blocking condition as the anode tocathode the voltage is reduced.



Elementary circuit for obtaining VI Characteristics of SCR

4.2 SCR CHARACTERISTICS

Latching current IL is the minimum anode current required to maintain the thyristor in the on-state immediately after the thyristor has been turned on and the gate signal has been removed.The VI characteristics of thyristor is shown below.



Once a thyristor conducts, it behaves like a conducting diode and there is no control over a

device. The device will continue to conduct. Because there is no depletion layer on the junction

J2 due to free movements of carriers. However, if the forward anode current is reduced below

Ha level known as holding current I , a depletion region will develop around junction J2 due to

the reduced number of carriers and the thyristor will be in the blocking state. The holding current

L H.is in the order of milliamperes and is less than the latching current IL. That is I >I Holding

current is the minimum anode current to maintain the thyristor in on-state.

When the cathode voltage is positive with respect to the anode, the junction J2 is forward biased,

but junction J1 and J3 are reverse biased. The thyristor will be in reverse blocking state and a

Rreverse leakage current known as reverse current I , would flow through the device.

AK BOA thyristor can be turned ON by increasing the forward voltage V beyond V , but such a

BOturn on could be destructive. In practice the forward voltage is maintained below V and the

thyristor is turned on by applying a positive voltage between gate and cathode. Once a thyristor

is turned on by a gating signal and its anode current is greater than the holding current the device.

Continues to conduct due to positive feedback, even if the gating signal is removed. A thyristor

is a latching device.



4.3 DEVICE TESTING PROCEDURE

SCR

1. Set the multimeter to diode mode of operation.

2. Connect multimeter voltage terminal to gate terminal of SCR.

3. Connect multimeter common terminal to cathode terminal of SCR.

4. Multimeter will show the low resistance value (typical 40 to 120S).

5. Remaining any of two combination will show the very much high value resistance (or)open.



4.4 PRECAUTIONS

Before doing the installation check out the below mentioned apparatus.

# VI characteristics of SCR trainer module (PEC16M1B).

Do’s

i. Ensure the fuses are in good condition.

ii. Switch ON the power.

iii. Ensure the input supply 230V AC, 50Hz signal.

iv. Whenever doing the connections make sure that all switches are in OFF condition.

v. Make the connections as per the connection procedure.

vi. Switch ON the power and SPDT switches.

vii. Do the experiment as per the experimental procedure.

Dont's

i. Do not short connectors P1 and P2.ii. Do not short connectors P14 and P15.

4.5 SERVICE TIPS

* Check for 18V AC signal at VDC1,else replace 230V/18V transformer (or) rectifier.

* Check for 24V AC signal at VDC2,else replace 230V/24V transformer (or) rectifier.

* Check for voltage variation up to 24V (VDC2) else replace POT3 (or) Regulator.

* Check for the fine and coarse adjustment of the gate voltage (VDC1) else replace POT2and POT1 respectively.(or) Regulator

* Check for the SCR device by following the device testing procedure else replace SCRdevice. If it fails, replace the SCR device.

vi characteristics of scr

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